iscsi: do not leak acb->buf when commands are aborted

acb->buf is freed in the WRITE(16) callback, but this may not
get called at all when commands are aborted.  Add another
free in the ABORT TASK callback, which requires setting acb->buf
to NULL everywhere.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
iscsi: add support for iovectors

This patch adds support for directly passing the iovec
array from QEMUIOVector if libiscsi supports it (1.8.0
or newer).

Signed-off-by: Peter Lieven <pl@kamp.de>
[Preserve the improvements from commit 4cc841b, iscsi: partly
 avoid iovec linearization in iscsi_aio_writev, 2012-11-19 - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Revert "serial: fix retry logic"

This reverts commit 67c5322d7000fd105a926eec44bc1765b7d70bdd:

    I'm not sure if the retry logic has ever worked when not using FIFO mode.  I
    found this while writing a test case although code inspection confirms it is
    definitely broken.

    The TSR retry logic will never actually happen because it is guarded by an
    'if (s->tsr_rety > 0)' but this is the only place that can ever make the
    variable greater than zero.  That effectively makes the retry logic an 'if (0)

    I believe this is a typo and the intention was >= 0.  Once this is fixed thoug
    I see double transmits with my test case.  This is because in the non FIFO
    case, serial_xmit may get invoked while LSR.THRE is still high because the
    character was processed but the retransmit timer was still active.

    We can handle this by simply checking for LSR.THRE and returning early.  It's
    possible that the FIFO paths also need some attention.

    Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
    Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

Even if the previous logic was never worked, new logic breaks stuff -
namely,

 qemu -enable-kvm -nographic -kernel /boot/vmlinuz-$(uname -r) -append console=ttyS0 -serial pty

the above command will cause the virtual machine to stuck at startup
using 100% CPU till one connects to the pty and sends any char to it.

Note this is rather typical invocation for various headless virtual
machines by libvirt.

So revert this change for now, till a better solution will be found.

Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Merge remote-tracking branch 'bonzini/scsi-next' into staging

# By Paolo Bonzini (1) and Peter Lieven (1)
# Via Paolo Bonzini
* bonzini/scsi-next:
  iscsi: add support for iovectors
  iscsi: do not leak acb->buf when commands are aborted